We propose a quantum secure direct communication protocol utilizing four-qubit cluster state to enhance the efficiency of eavesdropping detection. In the security analysis, by applying the method of the entropy theory, we contrast our scheme to another two strategies, the Ping-pong protocol and the protocol using two particles of Einstein–Podolsky–Rosen pair as detection particles. The comparison results show that if the eavesdropper obtains the same amount of information, the presented quantum protocol strategy will have a larger detection probability than the other two. At last, the security of the proposed protocol is discussed. The analysis results indicate that the protocol in this paper is more secure. Copyright © 2013 John Wiley & Sons, Ltd.